Twin super-scopes join forces to spy on early solar system

Like other T Tauri stars, the young DG Tau is surrounded by a disk that could eventually spawn planets.

NASA / JPL

July 17, 2003One of the major aspirations of modern astronomy is to capture the feeble light from Earth-sized planets orbiting distant stars. Taking a giant step closer to this lofty goal, a team of astronomers has combined the infrared light collected by two of the world's largest observatories and detected a ring of gas and dust swirling around a star more than 450 light-years distant.

By linking the twin 10-meter Keck telescopes on Mauna Kea in Hawaii in October 2002 and February 2003, the astronomers made detailed measurements of the young star DG Tau and its surrounding disk of hot material. The infrared observations reveal that, while the orbiting disk extends more than 4.5 billion miles from the star (as expected), its inner edge surprisingly lies at least 11 million miles from the central star.

Of the more than 100 extrasolar planets discovered, about a quarter of them lie within 10 million miles of their host star. However, DG Tau has no protoplanetary material that close to itself. The larger-than-anticipated gap between DG Tau and its disk leads astronomers to speculate that either DG Tau's disk is unusually far or that close-in planets have formed farther from their stars and eventually migrated inward.

"Studies like this teach us more about how stars form … and how planets eventually form in disks around stars," states Rachel Akeson, leader of the research team and astronomer at the California Institute of Technology in Pasadena.

The two large Keck telscopes can combine their light-gathering power through interferometry to probe the universe deeper than any other optical telescope system on Earth.

NASA / JPL

DG Tau is a "T Tauri" star, a newborn at the youngest observable stage in its life that has yet to begin burning its hydrogen core. Brighter T Tauri stars have been seen before, but the powerful resolution of the Keck Interferometer now allows astronomers to study fainter ones like DG Tau, says Akeson.

Thanks to an amazing technique called interferometry, the giant Keck mirrors work together as a single 85-meter glass, resolving finer detail than ever before. While observing the same object, the light collected by the individual telescopes is combined to create a constructive interference pattern. It would be like throwing one rock after another into a lake at just the right pace to create a set of ripples that join up and form a larger, more powerful set of waves.

The results, to be published in an upcoming issue of The Astrophysical Journal Letters, are the first published science observations by the Keck Interferometer. These findings also represent the first complete scientific study using an interferometer in combination with adaptive optics.

Andrew Fazekas is an astronomy columnist based in Montreal, Canada, who frequently writes for magazines, newspapers, and the Canadian Space Agency. He currently does science news commentary for both radio and television, teaches backyard astronomy at Vanier College, and is an editor at the American Association for the Advancement of Science.